Method and apparatus for vertical transfer of a semiconductor wafer cassette

ABSTRACT

A method and apparatus for removing a semiconductor wafer cassette from a SMIF pod and for transferring the cassette along a vertical axis to a platform of a wafer processing station. The apparatus is comprised of a transfer device that includes a pair of gripping arms for gripping the wafer cassette from the sides of the cassette. Once gripped, the cassette moves with the transfer device upward along a vertical axis to make room for the platform to be extended from within the processing station to a position under the cassette. Thereafter, the direction of motion of the transfer device is reversed and the cassette is lowered onto the platform. Once seated on the platform, the gripping arms retract from the cassette, and the cassette is carried on the platform into the processing station.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to the following copending U.S. PatentApplications:

Patent application Ser. No. 08/311,954 entitled, "SEMICONDUCTOR WAFERCASSETTE, " by Bonora et al., filed Sep. 26, 1994;

Patent application Ser. No. 08/394,698 entitled, "STANDARD MECHANICALINTERFACE VACUUM LOADLOCK CHAMBER, " by Bonora et al., filed Feb. 27,1995, now U.S. Pat. No. 5,586,585.

The above patent applications are owned by the assignee of the presentinvention and are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transfer device for use withstandardized mechanical interface (SMIF) systems for facilitatingsemiconductor wafer fabrication, and in particular to a transfermechanism for gripping and transport of a semiconductor wafer cassettealong a vertical axis.

2. Description of the Related Art

A SMIF system proposed by the Hewlett-Packard Company is disclosed inU.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system isto reduce particle fluxes onto semiconductor wafers during storage andtransport of the wafers through the semiconductor fabrication process.This purpose is accomplished, in part, by mechanically ensuring thatduring storage and transport, the gaseous media (such as air ornitrogen) surrounding the wafers is essentially stationary relative tothe wafers and by ensuring that particles from the ambient environmentdo not enter the immediate wafer environment.

The SMIF system provides a clean environment for articles by using asmall volume of particle-free gas which is controlled with respect tomotion, gas flow direction and external contaminants. Further details ofone proposed system are described in the paper entitled "SMIF: ATECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING, " by MihirParikh and Uirich Kaempf, Solid State Technology, July 1984, pp.111-115.

Systems of the above type are concerned with particle sizes which rangefrom below 0.02 μm to above 200 μm. Particles with these sizes can bevery damaging in semiconductor processing because of the smallgeometries employed in fabricating semiconductor devices. Typicaladvanced semiconductor processes today employ geometries which areone-half micron (μm) and under. Unwanted contamination particles whichhave geometries measuring greater than 0.1 μm substantially interferewith 1 μm geometry semiconductor devices. The trend, of course, is tohave smaller and smaller semiconductor processing geometries which todayin research and development labs approach 0.2 μm and below. In thefuture, geometries will become smaller and smaller and hence smaller andsmaller contamination particles become of interest.

A SMIF system has three main components: (1) sealed pods, having aminimal volume, used for storing and transporting cassettes which holdthe semiconductor wafers; (2) enclosures placed over cassette ports andwafer processing areas of processing equipment so that the environmentsinside the pods and enclosures (after having clean air sources) becomeminiature clean spaces; and (3) a transfer mechanism to load/unloadwafer and/or wafer cassettes from a sealed pod without contamination ofthe wafers in the wafer cassette from external environments.

It is important that a precisely controllable system be provided fortransferring wafer cassettes from, for example, a SMIF pod to within asemiconductor wafer processing station in order to avoid damaging thewafers within the cassette. Any such damage may be significant as asingle cassette may presently carry as much as $20,000 to $30,000 worthof 200 mm wafers.

There are presently several known schemes for transferring asemiconductor wafer cassette into a wafer processing station. Two commonschemes are shown in FIGS. 1A and 1B, respectively. In the system ofFIG. 1A, after a semiconductor wafer cassette 20 has been separated froma SMIP pod (not shown), the cassette may be loaded into a cassettechamber 22 of a wafer processing station 24 by first vertically raisingor lowering the cassette along a Y-axis to the properly align thecassette with the cassette chamber, and second by horizontally movingthe cassette along an X-axis into the cassette chamber.

The system of FIG. 1B differs from the system of FIG. 1A in that theprocessing station 24 includes a platform 26 that extends out of thecassette chamber 22 when a cassette is to be loaded into the chamber. Insome processing stations, the wafer cassette is desirably loaded deepwithin the cassette chamber. In such instances, the wafer cassettetransfer device may load the cassette on to the extended platform, whichplatform may then be retracted into the cassette chamber with thecassette supported thereon. In the system of FIG. 1B, after the cassetteis positioned adjacent to the processing station 24, the cassette 20need only be moved vertically along the Y-axis until the cassette islocated above the platform, and then lowered along the Y-axis onto theplatform after the platform has been extended. Thus, the system of FIG.1A requires a transfer mechanism capable of moving in both the X and Ydirections, whereas the system of FIG. 1B requires a transfer mechanismcapable of moving solely in the Y direction.

A conventional transfer mechanism for locating a cassette within aprocessing station cassette chamber for the systems of both FIGS. 1A and1B is shown in FIG. 1C. A SMIF pod, including a top 34 and a door 36 forsupporting the wafer cassette 20, is positioned on an indexer 38. Theindexer first decouples the pod top from the pod door, and then lowersthe pod door with the cassette thereon adjacent to the cassette chamber22 of the processing station 24. Thereafter, a pivotally mounted robotictransfer arm 40 transfers the cassette 20 from the pod door 36 on theindexer to a cassette platform 42 (FIG. 1C) within the chamber 22, or anextended platform 26 (FIG. 1B) outside of the chamber 22. A top grippingmechanism 44 is provided on the free end of the arm 40 for gripping afeatures conventionally provided on a top surface of the cassette 20.

For a processing station such as that shown in FIGS. 1A and 1C, atransfer mechanism such as described above capable of transporting acassette in both the X and Y directions is necessary in order to load acassette into the cassette chamber. However, where movement of thecassette is required only in the Y direction, such as where a processingstation includes an extendable platform as shown in FIG. 1B, a moresimple and space efficient design may be accomplished.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a simpleand space efficient automated system for transferring a semiconductorwafer cassette from a SMIF pod onto a platform of a wafer processingstation.

It is a further object of the present invention to provide a simple andspace efficient automated system for transferring a semiconductor wafercassette along a vertical axis.

It is another object of the present invention to provide an automatedsystem for transferring a semiconductor wafer cassette by gripping thecassette from the sides of the cassette.

These and other objects are accomplished by the present invention whichrelates to a method and apparatus for removing a semiconductor wafercassette from a SMIF pod and for transferring the cassette along avertical axis to a platform of a wafer processing station. Duringtransport and storage of a wafer cassette, the cassette is supportedwithin a pod which is comprised of a pod door on which the cassetterests, and a pod top which mates with the pod door to provide a sealedenvironment within the pod. According to the present invention, a SMIFpod carrying a cassette is loaded onto a transfer device lying on acommon vertical axis with the platform when the platform is extended.

The pod is loaded on the transfer device such that the pod door lies incontact with a port door of the transfer device, and the pod top lies incontact with a port plate surrounding the port door.

The pod top is thereafter secured to the port plate by a pair oflatches, and the pod door is decoupled from the pod top by a decouplingmechanism in the port door. Once decoupled, the port plate is movedupward relative to the port door so that the pod top supported on theport plate is separated from the pod door and cassette, which remainstationary with respect to the pod door.

At some point during the upward movement of the port plate, a pair ofgripping arms pivotally mounted within the port plate reside insubstantially the same horizontal plane as a pair of extensions, orears, formed on opposite sides of the cassette. At this point, relativemovement between the port plate and cassette is halted, and the grippingarms are pivoted inward to engage the ears of the cassette. Upon suchengagement, upward movement of the port plate is resumed so that thecassette is transported upward with the port plate along a verticalaxis.

The cassette is raised to an elevation sufficient to allow the platformretracted within the processing station cassette chamber to extend outof the chamber and under the cassette. Thereafter, the vertical motionof the port plate is reversed and the cassette is lowered along avertical axis onto the platform, whereupon the gripping arms retractback into their recessed position within the port plate. Once located onthe platform, the platform may be retracted to bring the cassette intothe processing station cassette chamber, whereupon the wafer process tobe performed within the station may be initiated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1A is a side view of a cassette loaded into a cassette chamber of aprocessing station;

FIG. 1B is a side view of a cassette loaded onto a platform of aprocessing station;

FIG. 1C is a side view of a conventional wafer cassette transfermechanism for loading a cassette into a cassette chamber of a waferprocessing station;

FIG. 2A is a front view of a wafer cassette within a SMIF pod as it isinitially loaded onto a cassette transfer mechanism according to thepresent invention;

FIG. 2B is a side view of a wafer cassette within a SMIF pod as it isinitially loaded onto a cassette transfer mechanism according to thepresent invention mounted proximate to a cassette chamber of a waferprocessing station;

FIGS. 3A and 3B are front views of a wafer cassette being separated froma SMIF pod by the transfer mechanism according to the present invention;

FIG. 3C is a side view of a wafer cassette being separated from a SMIFpod by the transfer mechanism according to the present invention mountedproximate to a cassette chamber of a wafer processing station;

FIG. 4A is a perspective view of the transfer mechanism according to thepresent invention including gripping arms for gripping a wafer cassette;

FIG. 4B is a top view of the gripping arms according to the presentinvention;

FIG. 5A is a front view of a wafer cassette being gripped by thetransfer mechanism gripping arms according to the present invention;

FIG. 5B is a side view of a wafer cassette being gripped by the transfermechanism gripping arms according to the present invention mountedproximate to a cassette chamber of a wafer processing station;

FIG. 6A is a front view of a wafer cassette being gripped by thetransfer mechanism gripping arms according to the present invention witha processing station platform positioned under the cassette;

FIG. 6B is a side view of a wafer cassette being gripped by the transfermechanism gripping arms according to the present invention with aprocessing station platform positioned under the cassette;

FIG. 7 is a side view of a wafer cassette located on top of a processingstation platform;

FIG. 8 is a side view of a wafer cassette located on top of a processingstation platform within a cassette chamber of the processing station;and

FIG. 9 is a side view of a sealed SMIF pod after a wafer cassette hasbeen located within a cassette chamber of a wafer processing station.FIG. 10 is a front view of a wafer cassette being gripped by thetransfer mechanism gripping arms according to an alternative embodimentof the invention.

DETAILED DESCRIPTION

The invention will now be described with reference to FIGS. 2A through9, which in general relate to a transfer device for transferring a wafercassette including one or more semiconductor wafers from a SMIF podalong a vertical axis to an extendable semiconductor processing stationplatform. While the present invention is described with respect to aSMIF system, it is understood that the present invention may be usedwith any of various pods for storing and transferring semiconductorwafers. As explained below, it is additionally contemplated that thepresent invention operate without a pod, so that a wafer cassette isloaded directly onto the transfer mechanism. The term "semiconductorwafer" or "wafer" as used herein refers to a wafer substrate as it mayexist in any of the various stages of the semiconductor waferfabrication process.

Referring now to FIG. 2A, there is shown a SMIF pod 100 comprised of apod door 102 and a pod top 104. The pod door mates with the pod top todefine a sealed environment in which a wafer cassette 106 carrying oneor more wafers 108 may be stored and transported. Although the presentinvention will be described herein with respect to transferring wafercassettes sized to hold 200 mm wafers, it is understood that the presentinvention may be configured to transfer wafer cassettes sized to acceptother size wafers, such as for example 150 mm and 300 mm wafers.

In order to transfer the cassette 106 from within the SMIF pod 100 towithin a processing station, the SMIF pod 100 is located on a transferdevice 110 according to the present invention which includes a port door112, a port plate 114 surrounding the port door 112, a pair of grippingarms 116a and 116b within the port plate, support members 118a and 118bfor engaging lead screws 120a and 120b, and a pair of pod top restraintlatches 122a and 122b. A central processing unit ("CPU") (not shown) isprovided for controlling the operation of, and for monitoring feedbacksignals from, various components of the transfer device 110 as explainedhereinafter.

Referring now to FIGS. 2A and 2B, in preparation for transferring thecassette 106 into a cassette chamber 124 of a wafer processing station126, the pod 100 is manually or automatedly seated on top of thetransfer device 110. The top surface of the transfer device may includea plurality of angled guide blocks (not shown) to allow easy guidance ofthe pod into proper position on top of the loadlock chamber.

When properly located on top of the transfer device 110, the pod door102 lies in contact with the port door 112, and the outer rim of pod top104 lies in contact with the port plate 110. Pod top restraint latches122a and 122b are provided to secure the pod top 104 to the port plate114. Once the pod 100 is properly positioned on the transfer device, thelatches 122a and 122b are pivoted from a first, retracted position (notshown) to a second position shown in FIG. 2A. In the second position,the latches 122a and 122b positively secure the pod top to the portplate. The movement of the latches 122a and 122b between the first andsecond positions may be accomplished by a conventional solenoid ormotor, the operation of which solenoid or motor is controlled by theCPU.

After the latches 122a and 122b have secured the pod top 104 to the portplate 114, the pod top 104 is decoupled from the pod door 102. This maybe accomplished by a decoupling mechanism provided in the port door 112.Details relating to a decoupling mechanism 122 for use with the presentinvention are described in U.S. Pat. No. 4,995,430, entitled "SealableTransportable Container Having Improved Latch Mechanism", whichapplication is assigned to the owner of the present application and isincorporated by reference in its entirety herein. As would beappreciated by those skilled in the art, the decoupling mechanism may becomprised of structures other than that disclosed in theabove-identified patent. It is further understood that, in alternativeembodiments, the decoupling mechanism may decouple the pod top from thepod door before or during pivoting of the latches 122a and 122b to therestraining position.

Referring now to FIGS. 3A-3C, after the pod top 104 has been decoupledfrom the pod door 102, the port plate is moved in an upward direction bymeans of support members 118a, 118b and lead screws 120a, 120b (FIG. 3Aand 3B). Support members 118a, 118b include a threaded opening throughwhich the lead screws 120a, 120b are provided such that rotation of leadscrews 120a, 120b together in one direction will raise the port plate114, and rotation of the lead screws 120a, 120b together in the oppositedirection will lower the port plate. The pod top 104, supported on theport plate 114, moves upward with the port plate. The pod door 102 andthe cassette 106, supported on the port door 112, remain stationary. Aswould be appreciated by those skilled in the art, structures other thansupport members 118a, 118b and lead screws 120a and 120b may be used toraise and lower the port plate 114. For example, FIG. 3C shows a singlesupport member 118 to which the port plate is mounted, which supportmember 118 is engaged with a single lead screw 120 located proximate tothe port plate 114. The rotation of the lead screw(s) may beaccomplished by a conventional driver such as a stepper or multi-polemotor, the operation of which is controlled by the CPU.

Referring now to FIGS. 4A-5B, at some point during the upward movementof the port plate 114, the gripping arms 116a, 116b will reside insubstantially the same horizontal plane as ears 130 on the cassette 106.The ears 130 are conventionally formed on a 200 mm wafer cassette,extending outward from opposite sides of the cassette 106. Once thegripping arms 116a, 116b are horizontally aligned with the ears 130,upward motion of the port plate 114 is halted and the gripping arms116a, 116b are pivoted inward toward ears 130 from their retractedposition within recesses 131a and 131b (FIG. 5A). The CPU may controlthe upward movement of the port plate 114 so as to stop the port plateafter it achieves an elevation which has been predetermined to align thegripping arms 116a, 116b with the ears 130. Alternatively oradditionally, the port plate 114 may include sensors (not shown) forsensing the relative position of the gripping arms to the cassette. Thesensors send a signal to the CPU to stop motion and to actuate thegripping arms when the sensors detect the proper orientation of thegripping arms 116a, 116b to the ears 130.

Gripping arms 116a, 116b each include a longitudinal member 132 having afirst end rotationally mounted to the port plate 114, and a gripping pad134 pivotally mounted on the free end of each longitudinal member 132.Each gripping pad 134 may include a slot 136 in which are received theears 130 when the gripping arms are pivoted into engagement with thecassette 106. The longitudinal members and the gripping pads arepreferably formed of rigid, durable, inert and stable materials such asfor example aluminum, stainless steel or any of several high-strengthpolymers including polyetheretherkeytone ("PEEK") or teflon®. Thelongitudinal members 132 may be formed of the same or different materialas the gripping pads 134.

The longitudinal members 132 may pivot with respect to the port plate114 by being mounted on shafts 138 rotationally mounted on bearings (notshown) within the port plate 114. As shown in FIG. 4A, the gripping arms116a, 116b are preferably mounted so as to rotate about a vertical axis.However, it is understood that the gripping arms may rotate about otheraxes. For example, the longitudinal members of the gripping arms may bemounted on shafts having axes that are parallel to the port plate 114 sothat the gripping arms pivot about a horizontal axis. In such anembodiment, the gripping pads 134 would be provided at an angle withrespect to the longitudinal members 132 so as to ensure that the slots136 properly mate with the ears 130. It is further understood that theshafts 138 may be stationarily mounted within the port plate 114, andthe longitudinal members rotationally mounted on the shafts. Aconventional drive system, such as a solenoid, stepper or multi-polemotor, or pneumatic mechanism, may cooperate with a conventional drivensystem, such as a worm gear, to pivot the gripping arms 116a, 116b intotheir position of engagement with the cassette, and back again to theirretracted position within recesses 131a, 131b (FIG. 5A). The operationof the drive system may be controlled by the CPU.

The gripping pads 134 may be pivotally mounted to the longitudinalmembers 132 by pins 140, which pins allow gripping pads 134 to pivotslightly with respect to the longitudinal member. Alternatively, as seenin FIG. 4B, the longitudinal members may each be comprised of four barlinkages such that the slots 136 of the gripping pads 134 are controlledto remain parallel to the ears 130 as the gripping arms pivot towardengagement with the cassette.

Gripping arm sensors (not shown) are preferably provided on either thegripping arms 116a, 116b or on the port plate 114 for sensing when thegripping arms 116a, 116b are in a home position, i.e., fully retractedwithin recesses 131a and 131b, respectively, and when the gripping armsare in an engaging position with the cassette. The gripping arm sensorsmay additionally sense when the gripping arms have pivoted past aposition where cassette engagement is anticipated, to thereafter stopfurther inward rotation of the gripping arms. Thus, for example where nocassette is present, the gripping arms will rotate inward and stop whenthe absence of the cassette is detected.

As shown in FIGS. 6A and 6B, after the cassette is gripped by thegripping arms 116a, 116b, the port plate resumes its upward motion atleast enough so that a platform 142, previously retracted within thecassette chamber 124, may be extended from the chamber to a positionunder the cassette 106. Operation of the platform may be controlled bythe CPU so that the platform 142 is extended once the port plate 114reaches a predetermined elevation. Alternatively or additionally,sensors (not shown) may be provided on the port plate and/or processingstation to indicate when the cassette has been sufficiently elevated toallow the platform to extend.

Once the platform 142 has extended, the direction of rotation of thelead screw(s) may be reversed, to thereby lower the cassette 106 ontothe platform 142 as shown in FIG. 7. Once the cassette 106 is positionedon the platform 142, the gripping arms 116a, 116b may disengage the ears130 and return to their retracted position within recesses 131a, 131b,respectively, within the port plate. The CPU may control the downwardmovement of the port plate 114 to stop after the cassette has beenlowered to an elevation which has been predetermined to locate thecassette on top of the platform. As stated above, the port plate 114and/or processing station 126 may alternatively or additionally includesensors (not shown) for sensing the relative position of the cassette tothe platform. The sensors send a signal to the CPU to stop the downwardmotion of the port plate when the sensors detect that the cassette isseated on the platform.

While the preferred embodiment of the present invention includes theabove-described gripping arms for gripping the ears formed on the wafercassette, it is understood that other gripping systems may be used togrip a cassette from the sides of the cassette, move the cassette alonga Y-axis until the cassette is at an elevation that allows a platform tobe located thereunder, and then to lower the cassette along the Y-axisonto the platform. For example, as described in U.S. patent applicationSer. No. 08/394,698 entitled, "STANDARD MECHANICAL INTERFACE VACUUMLOADLOCK CHAMBER", previously incorporated by reference, the presentinvention may include a pair of pawls mounted in the port plate forgripping a cassette by engaging slots formed in the sides of thecassette as the port plate moves upward. A cassette including such slotsis described in U.S. patent application Ser. No. 08/311,954 entitled,"SEMICONDUCTOR WAFER CASSETTE", previously incorporated by reference.

As shown in FIG. 8, after the platform 142 retracts into the cassettechamber 124, the port plate 114 may move downward to reunite the poddoor 102 with the pod top 104. Also, a door 144 on the processingstation 126 (shown in an open position) may seal the cassette chamber sothat the wafer process to be performed within the station 126 may beinitiated.

Although not critical to the present invention, a fluid circulationsystem 146 (FIGS. 7-9) may additionally be provided within a chamberdefinedby pod top 104, port plate 114, and the walls 148 of the transfermechanism 110. The fluid circulation system injects clean air into thechamber, which clean air flows out of openings in the chamber to theatmosphere surrounding the chamber. The positive flow of clean air outof the chamber openings prevents contaminants from the surroundingatmosphere from entering into the chamber through the openings.

Up to this point, the port door 112 and pod door 102 have been describedas remaining stationary while the port plate 114 and pod top 104 havebeen raised. However in an alternative embodiment of the invention, asshown in FIG. 10,the port door 112 may also be connected to an elevatormechanism 160 so as to move downward after the pod door has beenseparated from the pod top. In this embodiment, the port door movesdownward until the ears 130 on the cassette 106 lie in substantially thesame horizontal plane as the gripping arms 116a and 116b. At that point,the gripping arms 116a, 116b engage the cassette 106 as described above.Even in an embodiment where the port door lowers, the port plate muststill be capable of vertical movement so as to ensure that the cassetteis high enough to allow the platform 142 to extend, and then to lowerthe cassette 106 onto the platform. In a further embodiment, the portplate may be moved upward at the same time as the port door is moveddownward so as to achieve the desired alignment of the gripping arms116a, 116b with the ears 130 on the cassette.

In a still further embodiment of the invention, the cassette may beutilized without the SMIF pod 100. In this embodiment, the cassette 106may be located directly on top of the port door 112, and then the portplate 114 may be moved relative to the port door 112 until the grippingarms 116a, 116b lie in substantially the same horizontal plane as theears 130. Thereafter, the gripping arms grip and transfer the cassette106 as described above.

Although the invention has been described in detail herein, it should beunderstood that the invention is not limited to the embodiments hereindisclosed. Various changes, substitutions and modifications may be madethereto by those skilled in the art without departing from the spirit orscope of the invention as described and defined by the appended claims.

We claim:
 1. A method of transferring a wafer cassette from within aSMIF pod to a platform capable of extending out of a wafer processchamber to an extended position from a retracted position within thewafer process chamber, the SMIF pod including a pod top and a pod door,the pod door supporting the wafer cassette, the method comprising thesteps of:(a) positioning the SMIF pod on an indexer while the platformis in the retracted position, the indexer located along a substantiallycommon vertical axis with the platform when the platform is in theextended position; (b) separating the pod door from the pod top afterthe SMIF pod is positioned on the indexer in said step (a); (c) raisinga port plate of the indexer and the pod top along the vertical axis withrespect to the wafer cassette; (d) gripping the cassette with grippingarms mounted in the port plate; (e) raising the cassette gripped in saidstep (d) along the vertical axis to a position higher than the positionof the platform; (f) lowering the cassette raised in said step (e) ontothe platform after the platform has been extended; and (g) disengagingthe gripping aims from the sides of the cassette gripped in said step(d).
 2. A method of transferring a wafer cassette from within a SMIF podto a platform capable of extending out of a wafer process chamber asrecited in claim 1, wherein said step (c) of raising the port plate andthe pod top along the vertical axis with respect to the wafer cassettecomprises raising the port plate while the wafer cassette remainsstationarily supported on the port door.
 3. A method of transferring awafer cassette from within a SMIP pod to a platform capable of extendingout of a wafer process chamber as recited in claim 1, wherein said step(d) of gripping the cassette by gripping arms mounted in the port platecomprises the step of pivoting the gripping arms from a retractedposition within the port plate to a position of engagement with thecassette.
 4. A method of transferring a wafer cassette from within aSMIF pod to a platform capable of extending out of a wafer processchamber as recited in claim 3, further comprising the step of sensingwhether the gappers have pivoted past an anticipated position ofengagement with the cassette.
 5. A method of transferring a wafercassette from within a SMIF pod to a platform capable of extending outof a wafer process chamber as recited in claim 4, further comprising thestep of ceasing farther pivoting if it is determined that the grippershave pivoted past an anticipated position of engagement with thecassette in said step of sensing whether the grippers have pivoted pastan anticipated position of engagement with the cassette.
 6. A method oftransferring a wafer cassette from within a SMIF pod to a platformcapable of extending out of a wafer process chamber as recited in claim1, wherein said step (c) of raising the port plate and the pod top alongthe vertical axis with respect to the wafer cassette comprises loweringthe wafer cassette while the port plate and pod top remain stationary.7. A method of transferring a wafer cassette from within a SMIP pod to aplatform capable of extending out of a wafer process chamber as recitedin claim 1, further comprising the step of sensing when the port platehas reached a predetermined elevation with respect to the cassette insaid step (c) for the gripping arms to grip the cassette.
 8. A method oftransferring a wafer cassette from within a SMIF pod to a platformcapable of extending out of a wafer process chamber as recited in claim1, further comprising the step of sensing when the cassette has beenraised to a position higher than the position of the platform in saidstep (e).
 9. A method of transferring a wafer cassette from within aSMIP pod to a platform capable of extending out of a wafer processchamber as recited in claim 1, further comprising the step of sensingwhen the cassette is supported on the extended platform in said step(f).
 10. A method of transferring a wafer cassette from within a SMIFpod to a platform capable of extending out of a wafer process chamber asrecited in claim 1, further comprising the step of circulating fluidaround the cassette.
 11. A method of transferring a container includinga plurality of wafers onto a platform, the platform capable of movingbetween a first position within a process chamber and a second positionextending out of the process chamber, comprising the steps of:(a)positioning the container on a support surface including an innersupport surface surrounded by an outer support surface; (b) moving theouter support surface away from the inner support surface and thecontainer along a vertical axis while the platform is in the firstposition; (c) gripping the container with a gripper mounted in the outersupport surface when the outer support surface has reached apredetermined elevation along the vertical axis with respect to thecontainer; (d) moving the container gripped in said step (c) away fromthe inner support surface along the vertical axis to an elevation abovethe elevation of the platform; (e) lowering the container raised in saidstep (d) onto the platform after the platform has been moved to thesecond position; and (f) disengaging the gripper from the container. 12.A method of transferring a container including a plurality of wafersonto a platform as recited in claim 11, wherein the container is locatedin a pod comprising a top mating with a bottom when the container ispositioned on the support surface in said step (a), further comprisingthe step of separating the top from the bottom before said step (b) ofmoving the outer support surface away from the inner support surface andthe container.
 13. A method of transferring a container including aplurality of wafers onto a platform as recited in claim 12, furthercomprising the step of moving the top with the outer support surface insaid step (b).
 14. A method of transferring a container including aplurality of wafers onto a platform as recited in claim 13, wherein thecontainer is supported on the bottom when the container is positioned onthe support surface in said step (a), further comprising the step ofmoving the container away from the bottom along the vertical axis insaid step (d) of moving the container away from the inner supportsurface.
 15. A method of transferring a container including a pluralityof wafers onto a platform as recited in claim 11, wherein said step (c)of gripping the container by a gripper comprises the step of pivotingthe gripper from a retracted position within the outer support surfaceto a position of engagement with the container.
 16. A method oftransferring a container including a plurality of wafers onto a platformas recited in claim 11, further comprising the step of sensing when theouter support surface has reached the predetermined elevation withrespect to the container in said step (b).
 17. A method of transferringa container including a plurality of wafers onto a platform as recitedin claim 11, further comprising the step of sensing when the containerhas been moved to a position above the elevation of the platform in saidstep (d).
 18. A method of transferring a container including a pluralityof wafers onto a platform as recited in claim 11, further comprising thestep of sensing when the container is supported on the platform when theplatform is in the second position in said step (e).